Microsuspension process for preparing solvent core sequential polymer dispersion

ABSTRACT

The present invention relates to a sequential polymerization process for preparing a water-insoluble dispersion of core/shell particles. In one embodiment the process may be employed to produce a particulate dispersion useful in making water-based coating compositions wherein on drying the particulate dispersion serves as an opacifying agent. In another embodiment the process may be employed to microencapsulate a hydrophobic target material, such as a biocide or herbicide.

This is a division of application Ser. No. 06/728,992 filed Apr. 30,1985 now U.S. Pat. No. 4,677,003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to both the coatings andmicroencapsulation arts and specifically to a sequential polymerizationprocess for preparing a water-insoluble dispersion of core/shellparticles. In one embodiment the process may be employed to produce aparticulate dispersion useful in making water-based coating compositionswherein on drying the particulate dispersion serves as an opacifyingagent. In another embodiment the process may be employed tomicroencapsulate a hydrophobic target material, such as a biocide orherbicide.

2. Brief Description of the Prior Art

Microvoid containing particles have previously been prepared by avariety of techniques.

For example, Kershaw, et al., U.S. Pat. No. 3,891,577, prepares avesiculated polymer by converting to a solid polymer, a liquid mediumcontaining dispersed therein particles of another polymer swollen by aliquid swellant, the liquid swellant then being at least partiallyremoved from the dispersed polymer particle. The liquid medium may beconverted to a solid by removal of solvent, e.g., from a solution of thesolid polymer, or preferably, by polymerization of a monomer,comonomers, or an oligomer or a mixture of these. Optionally, adissolved polymer may be present in the liquid to be polymerized.Solidification of the liquid in which these swollen particles aredispersed and removal of the swellant is then carried out to provide thevesiculated polymer, which may be in bulk form, as a film, or in theform of a coating applied to a substrate.

In another embodiment, Kershaw teaches that the dispersion of swollenpolymer in the liquid medium may itself be dispersed in a further liquidin which it is insoluble. The further liquid is referred to as thesuspending liquid. Solidification of the medium is then carried out andafter separation of the granules formed from the suspending liquid,liquid swellant may be removed from the swollen polymer to providevesiculated polymer in granular form. Alternatively, when, for example,the vesiculated granules are to be used in a coating composition withwhich the suspending liquid is compatible, the granules formed bysolidification of the medium may be incorporated into the composition asa slurry in at least part of the suspending liquid. On applying thecomposition to a substrate, formation of a coating film and removal ofswellant from the swollen dispersed polymer to form the vesicles withinthe granule then take place concurrently.

Kurth, et al., in U.S. Pat. No. 3,870,099, disclose the preparation ofsequential acrylic polymers containing 0.5-2.5% of an alpha,beta=unsaturated carboxylic acid. The bulk of the acid is introduced inthe early part of the polymerization.

Kowalski et al., in U.S. Pat. No. 4.427,836, disclose the production anduse of water-=insoluble particulate heteropolymers made by sequentialemulsion polymerization in dispersed particles of which a core of apolymeric acid is at least partially encased in a sheath polymer that ispermeable to a volatile base, such as ammonia or an organic amine,adapted to cause swelling of the core by neutralization. The sheath isnot permeable to permanent, non-volatile bases such as sodium hydroxide.The aqueous dispersion of the acid-containing core/sheath particles isuseful in making water-based coating composition wherein it may serve asan opacifying agent when the volatile base is used to at least partiallyneutralize neutralize the heteropolymer, microvoids being formed incores of the swollen particles and the film during the drying. Althoughthe core may be made in a single stage of the sequential polymerizationand the sheath may be the product of the single sequential stagefollowing the core stage, the making of the core component may involve aplurality of steps in sequence followed by the making of the sheathwhich also may involve a series of sequential steps. Thus the firststage of the emulsion polymerization in the process of the Kowalskiinvention may be the preparation of a seed polymer containing smalldispersed polymer particles insoluble in the aqueous emulsionpolymerization medium. This seed polymer, which may or may not containany acid component, provides particles of minute size which form thenuclei on which the core polymer of acid monomer, with or withoutnonionic comonomers, is formed. The polymer particles of this inventionare prepared by aqueous emulsion polymerization, which requires awater-soluble free radical initiator, or a mixture of such an initiatorwith a water-soluble reducing agent to form a redox system. In apreferred embodiment a seed polymer is used along with a low level ofcore stage emulsifier. By carrying out the emulsion polymerization whilemaintaining low levels of emulsifier, the subsequent stages of polymerformation deposit the most recently formed polymer on the existingdispersed polymer particles resulting from the preceeding step or stage.If the amount of emulsifier is kept below the amount corresponding tothe critical micelle concentration (CMC) for a particular monomersystem, a preferred unimodal product results. While the CMC may beexceeded somewhat without the formation of an objectionable or excessivenumber of dispersed micelles or particles, it is preferred that thenumber of micelles during the various stages of polymerization becontrolled so that the deposition of the subsequently formed polymer ineach stage occurs upon the dispersed micelles or particles formed in theprevious stages.

Kowalski et al., in related U.S. Pat. No. 4,469,825, disclosecore-sheath polymer particles wherein the core monomer system requiresan amine group-containing comonomer which comprises at least 5% byweight of the core monomer system.

Kowalski et al., in U.S. Ser. No. 590,082, filed Mar. 15, 1984, disclosea process for making core/sheath polymer particles in which the emulsionpolymerized core system may contain either a polymerizable carboxylicacid and/or amine, giving an acid or base functional core, and in whichthe sheath monomer system comprises monomers having no ionizable group.A hydrophobic material such as material selected from the siliconesurfactants, fluorocarbon surfactants, and hydrophobic non-vinylpolymerizable liquids, is employed in the polymerization process.

Blankenship et al., in U.S. Ser. No. 690,913, filed Jan. 11, 1985, nowU.S. Pat. No. 4,594,363 disclose a process for making core-sheathpolymer particles useful for opacifying coating films, comprising

(A) emulsion polymerizing a core from a core monomer system comprised ofat least one ethylenically unsaturated monomer containing acidfunctionality;

(B) encapsulating the core with a hard sheath by emulsion polymerizing asheath monomer system in the presence of the core, the sheath permittingpenetration of fixed or permanent bases;

(C) swelling at elevated temperature the resultant core-sheath polymerparticles with fixed or permanent base so as to produce a dispersion ofparticles which, when dried, contain a microvoid which causes opacity incompositions in which they are contained, provided that either (1) thesheath comprises at least about 1% acid functional monomer or (2) theswelling takes place in the presence of solvent.

Kowalski et al., in U.S. Pat. No. 4,468,498, discloses a process formaking an aqueous dispersion of core/sheath polymers in which the corecontains sufficient acid groups to render the core swellable byneutralization with a volatile base to at least twice its volume andwherein the sheath is permeable to the base.

Morehouse, Jr. et al., in U.S. Pat. No. 4,049,604, disclose aqueousdispersions of normally solid, organic polymeric particles that areprepared by (1) dispersing an oil phase containing at least one emulsionpolymerizable monomer such as styrene in an aqueous phase containing astabilizing emulsifier such as sodium dodecylbenzene sulfonate and acopolymer of a sulfo ester of an alpha, beta-ethylenically unsaturatedcarboxylic acid, such as 2-sulfoethyl methacrylate, and butyl acrylateand (2) subjecting the dispersion to emulsion polymerization.Microspheres having liquid centers and seamless rigid walls of thenormally solid, organic polymer are prepared according to this methodexcept that the starting oil phase also contains a nonpolymerizable,water-insoluble liquid such as hexane. The polymers of sulfo esters ofalpha, beta-ethylenically unsaturated carboxylic acids serve ascoalescence aids. The diameter of the resulting microspheres isinversely related to the concentration of the polymer of sulfo esteremployed (operable range: 0.2 to 2.0 weight percent). Microspheres bythis process have an average diameter of from about 0.5 to about 3microns, when the amount of sulfoester employed is at the upper end ofthe acceptable range. Microspheres of this size are suspensions and notdispersions, they will settle out of the aqueous medium on standing.

Ugelstad, in U.S. Pat. No. 4,336,173, discloses a process for preparingan aqueous emulsion or dispersion of a partly water-soluble material andoptionally further conversion of the prepared dispersion or emulsion toa polymer dispersion when the partly water-soluble material is apolymerization monomer. In the first step a dispersion of polymerparticles is prepared containing one or more materials having very lowsolubility in water, then in a second step there is added the partlywater-soluble material which diffuses into the particles from the firststep, and then, if the partly water-soluble material is a polymerizablemonomer, polymerization may be affected. By using a seed consisting of apolymer and essentially water-insoluble material, the seed particleswill be capable of absorbing much greater amounts of monomer, it oftenbeing possible to add all the monomer in one step, and the amount ofseed employed may be greatly reduced, in comparison with conventionalemulsion seeded polymerization. In the conventional process, the seedparticles consists of polymer molecules which are capable of absorbingonly one to four times their own volume in polymerizable monomer;however, the Ugelstad seed can absorb much greater amounts of monomer.Thus the tendency to form a second mode of unseeded polymer particlesduring the polymerization of the monomer swollen seeds is reduced.Either a water-soluble initiator such as potassium persulfate orhydrogen peroxide or an oil-soluble initiator such as lauryl peroxidemay be employed.

Ugelstad, in U.S. Pat. No. 4,113,687, disclosed a process for preparinga latex by efficiently homogenizing an aqueous mixture containing anemulsifier and a water-insoluble solvent for the monomer to bepolymerized, adding monomer and, if desired, further water to thehomogenized mixture and also water-soluble polymerization initiator.Instead of a water-soluble initiator, an oil soluble initiator may beused provided it has sufficient solubility diffused through the aqueousphase into the drops of water insoluble solvent and monomer.

Microencapsulation methods and the properties of the resultingmicrocapsulates are reviewed by T. Kondo in Surface and Colloid Science,Volume 10 (Plenum Press, New York 1978) pp. 1-41. Microencapsulation isalso reviewed by R. E. Sparks in Kirk-Othmer, Encyclopedia of ChemicalTechnology, Volume 15 (3rd Edition) pp. 470-491. Microencapsulation ofwater immiscible materials, such as aqueous dispersions of pesticidesand herbicides, is reviewed by Beestman et al. in U.S. Pat. Nos.4,417,916 and 4,280,833, in which an improved microencapsulation processemploying lignin sulfonate emulsifier and the reaction of polymethylenepolyphenylisocyanate and a polyfunctional amine is taught. R. C.Koestler, in U.S. Pat. No. 4,360,376, teaches an interfacialpolycondensation method of microencapsulating trifluralin, apre-emergent herbicide. H. B. Scher et al., in U.S. Pat. No. 4,155,741,discloses a stable suspension-buffer system for aqueous suspensions ofpolyurea-microencapsulated materials, including herbicides andinsecticides, which can be obtained by using aluminum hydroxide orferric hydroxide as suspending agent, thereby preventing separation andcaking in flowable microcapsule formulations.

SUMMARY OF THE INVENTION

The present invention provides an improved process for producing aqueousdispersions of polymeric core/shell particles prepared by sequentialmicrosuspension polymerization having a core containing a solvent blend.These particles are useful in opacifying film formed by aqueous coatingcompositions through microvoid formation. This invention also providesan improved process for microencapsulation of organic target materialsin an aqueous dispersion of water-insoluble core/shell particles.Because an aqueous medium is employed rather than an organic solvent forthe preparation of the microcapsule walls, the aqueous dispersions ofmicroencapsulated target materials may be advantageously used directlyin many applications, such as in preparing for agricultural use aqueoustank mixes of encapsulated pesticides and non-encapsulated fertilizer.These and other advantages of the present invention, which will beapparent from the disclosure below, are met by the present invention,which is a process for preparing an aqueous dispersion ofwater-insoluble core/shell particles comprising

(a) preparing core emulsion by emulsifying in water at high shear

(1) at least one hydrophilic solvent,

(2) at least one hydrophobic solvent,

(3) initial monomer comprising at least two polymerizable mono-alpha,beta-ethylenically unsaturated compounds wherein said initial monomerincludes from about 2 to 4% by weight, based on the total weight of saidinitial monomer of alpha, beta-ethylenically unsaturated carboxylic acidmonomer,

(4) anionic surfactant

(5) water-insoluble emulsion stabilizer, and

(6) water-insoluble thermal polymerization initiator,

wherein said hydrophobic and hydrophilic solvents or non-solvents for apolymer prepared by polymerizing said initial monomer,

(b) heating said core emulsion to polymerize said initial monomer,thereby forming core particles,

(c) adding at least one base selected from ammonia and the organicamines thereby neutralizing polymerized carboxylic acid and formingcore/shell particles, and

(d) optionally adding additional monomer whereby said additional monomeris polymerized on said core/shell particles.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a process for polymerizationemploying an oil-soluble polymerization initiator, such as laurylperoxide. Because an oil-soluble initiator, as opposed to an initiatorsoluble in water or slightly soluble in water is employed, the processcan be referred to as a suspension polymerization technique as opposedto an emulsion polymerization process. The oil-soluble initiator, amixture of hydrophobic and hydrophilic solvents, anionic surfactant, andwater-insoluble emulsion stabilizer are emulsified in water at highshear along with initial monomer which comprises at least twopolymerizable mono-ethylenically unsaturated compounds to form a "core"emulsion. When it is desired to encapsulate an organic target material,such as a biocide or herbicide, the target material is included in themixture which is sheared to yield the core emulsion. The organic targetmaterial may be substituted for the hydrophobic solvent, or a mixture ofhydrophobic solvent and organic target materials may be used. Thehydrophilic and hydrophobic solvents and the mixture are nonsolvents forthe polymer which is prepared by polymerizing the initial monomer. Theinitial monomer includes from about 2% to 4% by weight, based on thetotal weight of the initial monomer, of alpha, beta-ethylenicallyunsaturated carboxylic acid monomer. The core emulsion is then heated topolymerize the initial monomer. Subsequently at least one base selectedfrom ammonia and the organic amines is added to the dispersion, therebyneutralizing the polymerized carboxylic acid and developing thecore-shell structure of the particles. Subsequently, optional additionalethylenically unsaturated monomer is added to the core/shell particledispersion.

It is believed that neutralization of the carboxylic acid inducespolymer carrying carboxylic acid functionality to migrate to theinterface between the aqueous medium and the core particles, creating acore/shell structure within the particles. However, the presentinvention is in no way limited by this explanation. The additionalmonomer is polymerized on or in the previously formed shell of thecore/shell particles, the polymerization of the additional monomer beinginitiated by residual water-insoluble thermal polymerization initiatorwithin the already formed core/shell particles.

In an alternative embodiment, additional initiator may be added to theaqueous dispersion of core particles prior to the addition of theadditional monomer. The additional polymerization initiator may also beadded concurrently with or subsequently to the addition of theadditional monomer. The additional polymerization initiator may be waterinsoluble, slightly water soluble or water soluble. When it is desiredto avoid or minimize the formation of a second mode of polymerparticles, polymerization of the additional monomer in the absence ofadditional polymerization initiator is preferred. It is preferred thatthe additional monomer composition be chosen so that additional monomerwhen polymerized forms a shell upon the pre-existing core particles.Examples of additional polymerization initiators which may be employedinclude polymerization initiators of the free radical type, such asammonium or potassium persulfate, which may be used alone or as theoxidizing component of a redox system, which also includes a reducingcomponent such as potassium metabisulfite, sodium thiosulfate or sodiumformaldehyde sulfoxylate. The reducing component is frequently referredto as an accelerator. The initiator and accelerator, commonly referredto as catalyst, catalyst system or redox system, may be used inproportion from about 0.01% or less to 3% each, based on the weight ofmonomers to be copolymerized. Examples of redox catalyst systems includet-butyl hydroperoxide/sodium formaldehyde sulfoxylate/Fe(II), andammonium persulfate/sodium bisulfite/sodium hydrosulfite/Fe(II). Thepolymerization temperature may be from room temperature to 90° C., ormore, and may be optimized for the catalyst system employed, as isconventional.

Chain transfer agents including mercaptans, polymercaptans andpolyhalogen compounds are sometimes desirable in the polymerizationmixture to moderate polymer molecular weight. Examples of chain transferagents which may be used include long chain alkyl mercaptans such ast-dodecyl mercaptans, alcohols such as isopropanol, isobutanol, laurylalcohol or t-octyl alcohol, carbon tetrachloride, tetrachloroethyleneand trichlorobromoethane. Generally from about 0 to 3% by weight, basedon the weight of the monomer mixture, may be used.

If desired, the addition and polymerization of the additional monomermay be omitted, provided that the initial monomer is selected to yieldpolymer having a calculated glass transition temperature (T_(g)) greaterthan about 70° C. Even when additional monomer is employed and ispolymerized on core/shell particles, it is preferred that the core/shellparticle polymer have a calculated T_(g) greater than about 70° C. TheT_(g) of a polymer with a specific monomer composition is determinablein a known manner either experimentally or by calculation. The method ofcalculating the T_(g) based upon the T_(g) of homopolymers of individualmonomers is described by Fox, Bull. Am. Physics Soc. 1,3, pg, 123(1956). Monomers may be selected to obtain the appropriate T_(g) throughuse of the "Rohm and Haas Acrylic Glass Transition TemperatureAnalyzer", Publication CM-24 L/cb of Rohm and Haas Company,Philadelphia, Pa. Examples of initial monomers which when polymerizedwill yield core polymer having a calculated T_(g) greater than about 70°C. are methyl methacrylate, styrene, and mixtures thereof. It ispreferred that the initial monomer comprise at least 80% by weight,based on the weight of initial monomer, of monomer selected from methylmethacrylate, styrene, and mixtures thereof. Initial monomer comprisingat least 50% by weight methyl methacrylate is especially preferred.

Examples of nonionic monoethylenically unsaturated monomers which may beemployed in preparing the core/shell particle includes styrene vinyltoluene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride,acrylonitrile, (meth)acrylamide, various (C₁ -C₂₀) alkyl or (C₃ -C₂₀)alkenyl esters of (meth)acrylic acid; for example, methyl methacrylate,methyl acrylate, ethyl (meth)acrylate, butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, lauryl(meth)acrylate, oleo (meth)acrylate, palmityl (meth)acrylate, andstearyl (meth)acrylate. The expression (meth)acrylic acid is intended toserve as a generic expression embracing both acrylic and methacrylicacid. Similarly, the expression (meth)acrylate is intended as a genericexpression embracing both acrylic acid and methacrylic acid esters.

Examples of alpha, beta-ethylenically unsaturated carboxylic acidmonomer which may be used to prepare the core/shell particles includeacid monomers such as methacrylic acid, beta-acryloxypropionic acid,mixtures of beta-acryloxypropionic acid and higher oligomers of acrylicacid, methacryloxypropionic acid, itaconic acid, citraconic acid,crotonic acid, maleic acid or maleic anhydride, fumaric acid, monomethylmaleate, monomethyl fumarate and monomethyl itaconic, and mixturesthereof and mixtures of methacrylic and acrylic acids. The preferredacid monomers that may be employed in preparing the core particles ofthe present invention are methacrylic acid and mixtures of acrylic acidand methacrylic acid, especially preferred is methacrylic acid. It ispreferred that the methacrylic acid comprise from about 21/4to 3% byweight, based on the total weight of initial monomer, of the initialmonomer. Other preferred acid monomers that may be used includeacryloxypropionic acid, and mixtures of acryloxypropionic acid and thehigher oligomers of acrylic acid.

It is preferred that the initial monomer used to prepare the core/shellparticles comprise up to 10% by weight, based on the total weight ofinitial monomer, of monomer selected from the group consisting of ethylacrylate, acrylonitrile and mixtures thereof. Ethyl acrylate isespecially preferred. When ethyl acrylate is employed, it is preferredthat about 5% by weight, based on the total weight of initial monomer,be used.

The hydrophobic solvent used in preparing the core particle ispreferably selected from the acyclic paraffinic hydrocarbons, mixturesof the acyclic paraffinic hydrocarbons and cyclic paraffinichydrocarbons and mixtures of acyclic paraffinic hydrocarbons, cyclicparaffinic hydrocarbons and aromatic hydrocarbons wherein the mixturescontain less than about 10% by weight, based on the total weight of themixture, of aromatic hydrocarbons. Examples of hydrophobic solventswhich may be employed include mineral spirits, petroleum spirits,ligroin, VM&P naphtha (varnish maker's and painter's naphtha), refinedsolvent naphtha, solvent naphtha, petroleum and petroleum benzin. It ispreferred that the 50% distillation temperature of the hydrophobicsolvent be from about 150° C. to 20° C. It is especially preferred thata hydrophobic solvent with a 50% distillation temperature of from abut150° C. to 180° C. be employed in the process of preparing the coreparticles. It is also preferred that the hydrophobic solvent be amixture of acyclic paraffinic hydrocarbons and cyclic paraffinichydrocarbons wherein the cyclic paraffinic hydrocarbons comprise no morethan about 5% by weight of the mixture.

The hydrophilic solvent employed in preparing the core particle ispreferably selected from the isomers of butanol, pentanol, hexanol, andmethyl isobutyl carbitol and mixtures thereof. When the hydrophilicsolvent is a hydroxyl compound, it is preferred that the proportion ofhydrophilic solvent to hydrophobic solvent be chosen so that there arefrom about 0.28 to about 0.42 moles of hydroxyl functionality per 100gms of hydrophilic/hydrophobic solvent blend. It is especially preferredthat the proportion of hydrophilic to hydrophobic solvent be chosen togive 0.34 moles of hydroxyl functionality per 100 gms of solvent blend.For example, when pentanol is chosen as the hydrophilic solvent to beemployed, the weight ratio of hydrophilic to hydrophobic solvent ispreferably from about 1:3 to about 9:11, and a ratio of about 3 to 7 isespecially preferred. When butanol is selected as hydrophilic solvent, aratio of hydrophilic to hydrophobic solvent of about 1 to 3 isespecially preferred. When hexanol is chosen as hydrophilic solvent, aweight ratio of hydrophilic to hydrophobic solvent of about 3.5 to 6.5is especially preferred.

An anionic surfactant such as an alkali metal salt of a di(C₇-C₂₅)alkylsulfosuccinates or of an alkyl aryl sulfonate, is employed asan aid in preparing the initial dispersion of initial monomer, solventmixture (including organic target material, if desired), and emulsionstabilizer.

Examples of suitable anionic dispersing agents include, for example, thehigher fatty alcohol sulfates, such as sodium lauryl sulfate, and thelike; alkylaryl sulfonates such as sodium or potassium isopropylbenzenesulfonates or isopropyl naphthalene sulfonates, and the like; alkalimetal higher alkyl sulfosuccinates, such as sodium octyl sulfosuccinate,sodium N-methyl, N-palmitoyltaurate, sodium oleyl isothionate, and thelike; and alkali metal salts of alkylarylpolyethoxyethanol sulfates,sulfonates or phosphates, such as sodiumtert-octylphenoxypolyethoxyethyl sulfates and nonyl phenoxypolyethoxyethyl phosphates, either having 1 to 7 oxyethylene units, and the like.An example of a preferred alkali metal salt dioctylsulfosuccinate issodium dioctyl sulfosuccinate. An example of a preferred alkylbenzenesulfonate is sodium dodecylbenzene sulfonate. It is preferred that theanionic surfactant comprise from about 0.2 to 0.8% by weight of theorganic phase of the core emulsion. It is especially preferred that theanionic surfactant comprise from about 0.3 to 0.5% by weight of theorganic phase of the core emulsion.

The water-insoluble emulsion stabilizer may be selected from organiccompounds having a molecular weight of less than about 500 and a watersolubility of less than about 10⁻⁴ gms per liter. The water-insolubleemulsion stabilizer is preferably selected from the di(C₄ -C₁₀)alkylphthalates, dibutoxyethyl phthalate, n-butyl benzyl phthalate,dimethylcyclohexyl phthalate, dicyclohexyl phthalate, diphenylphthalate, dipropyleneglyccol dibenzoate, diethyleneglycol dibenzoate,triethyleneglycol di-(2-ethylbutyrate), di-(2-ethylhexyl) adipate,di-isooctylazelate, di-(2-ethylhexyl)azelate, di-n-butyl sebacate,1-chlorododecane, hexadecane, and mixtures thereof. An especiallypreferred water-insoluble emulsion stabilizer isdi(2-ethylhexyl)phthalate (a/k/a dioctyl phthalate). It is preferredthat the water-insoluble emulsion stabilizer comprise at least about0.25% by weight of the organic phase of the core emulsion. It isespecially preferred that the water-insoluble emulsion stabilizercomprise from about 2.5 to 4% by weight of the organic phase of the coreemulsion.

The core emulsion contains a water-insoluble thermal polymerizationinitiator such as lauryl peroxide. The ratio of the weight of thewater-insoluble thermal polymerization initiator to the total weight ofinitial monomer employed in preparing the core emulsion is from about0.1:100 to 5:100. It is preferred that the ratio of the weight of thewater-insoluble thermal polymerization initiator to the total weight ofthe initial monomer be from about 2.5:100 to 4:100.

The core emulsion is prepared by adding the solvent blend, initialmonomer, emulsion stabilizer, anionic surfactant and water-insolubleinitiator to water and subjecting the mixture to high mechanicalshearing forces. The shear force may be applied mechanically as by useof a high shear mechanical disperser such as a Waring® Blender (Waringis a trademark of Dynamic Corp. of America) or high speed impeller asare commonly used in coatings manufacture. Alternatively, the high sheardispersion may be accomplished ultrasonically. The average particle sizeand particle size distribution of the core emulsion is believed todepend upon the magnitude and duration of the shearing forces applied.

In addition, the particle size distribution is believed to depend on thenature and relative amount of anionic surfactant used, the nature andamounts of the solvents employed, the nature and relative amounts of themonomers to be copolymerized, and the like.

When the polymerized dispersion is to ultimately be used to impartopacity, it is preferred that the average particle size of the coreemulsion after dispersion be from about 0.22 to 0.35 microns asdetermined by photon correlation spectroscopy. Light scatteringtechniques such as photon correlation spectroscopy measure the Z-averageparticle size. It is especially preferred that the average particle sizeof the core emulsion after dispersion be from about 0.27 to 0.32microns, when the polymerized dispersion resulting from the coreemulsion is to be used to impart opacity, as in coating compositions.

After the core emulsion has been formed, it is heated to activate thethermal water-insoluble polymerization initiator. The optimumpolymerization temperature depends upon the thermal initiator used toeffect the polymerization. When lauryl peroxide is employed the coreemulsion is preferably heated to a temperature of from about 86 to 89°C. Because the initial monomer and hydrophobic/hydrophilic solvent blendare chosen so that the polymer is formed from the initial monomersinsoluble in the solvent blend, it is believed that the polymer forms aseparate phase within the core emulsion when the initial monomer ispolymerized. After polymerization of the initial monomer, thecopolymerized residues of the acid monomer are neutralized by additionof a base selected from ammonia and a organic amines. Ammonia ispreferred to effect the neutralization.

Subsequent to the neutralization of the polymerized carboxylic acid,additional monomer may be added to the core/shell particles. It ispreferred that the additional monomer be selected to yield polymerhaving a calculated glass transition temperature greater than about 80°C. Any of the non-carboxylic acid monomers useful in preparing the corepolymer may be employed as additional monomer. Thus, for example, ethylacrylate, butyl acrylate, methyl methacrylate, styrene, andacrylonitrile may be employed. Mixtures of ethylenically unsaturatedmonomers, such as methyl methacrylate, butyl acrylate, and methylmethacrylate styrene mixtures may be used. Methyl methacrylate ispreferred. It is especially preferred that the additional monomercomprise at least about 80% by weight, based on the total weight of theadditional monomer, of methyl methacrylate.

The additional monomer may also comprise at least one multialpha,beta-ethylenically unsaturated monomer. It is preferred that when suchmulti-alpha, beta-ethylenically unsaturated monomer is employed itcomprise no more than about 5% by weight of the total additionalmonomer. Preferred multi-alpha, beta-ethylenically unsaturated monomersuseful as additional monomer are allyl (meth)-acrylate,tripropyleneglycol di(meth)acrylate, diethyleneglycol di(meth)acrylate,ethyleneglycol di(meth)acrylate, diethyleneglycol di(meth)acrylate,ethyleneglycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,1,3-butyleneglycol di(meth)acrylate, diallyl phthalate,trimethylolpropane tri(meth)acrylate, and divinylbenzene. Especiallypreferred multi-alpha, beta-ehtylenically unsaturated monomers are allylmethacrylate, diallyl phthalate, and trimethylolpropane trimethacrylate.

It is preferred that the weight ratio of solvent blend (that ishydrophilic plus hydrophobic solvents) to initial monomer be from about1:0.8 to 1:3. It is especially preferred that the ratio of solvent blendto initial monomer be about 1:1.3. It is preferred that the weight ratioof initial monomer to additional monomer be from about 0.9 to 1.5. It isespecially preferred that the weight ratio of initial monomer toadditional monomer be about 1.3:1.

The core/shell particles prepared by the process of the presentinvention are useful as opacifying agents in coatings compositions.Drying compositions which contain aqueous dispersions of thesecore/shell particles is believed to cause the formation of singleindividual voids within the core/shell particles which contribute to theopacity of the dried compositions containing the core/shell particles.When the core/shell particles of the present invention are used asopacifying agents, the amount of polymer deposited to form the shellpolymer is generally such so as to provide an overall particle size ofthe core/shell particle of from about 0.35 to 0.55 microns, preferablyfrom about 0.42 to 0.48 microns, and a polydispersity index of fromabout 1.5 to 5.

The core/shell particles of the present invention are useful for aqueouscoating and impregnating compositions such as those of U.S. Pat. No.2,795,564, as opacifying agents and such compositions either as asupplement to, or replacement of, pigmentary matter and/or extenderstherefor. For these purposes the aqueous dispersions of the core/shellpolymer may be added directly to the coating and or impregnatingcompositions. Alternatively, the core/shell polymers may be isolatedfrom the dispersions, by filtration or decantation, and then the organicsolvent blend may be removed as by drying or volatilization, underconditions such that microvoids are formed and retained in theindividual particles or granules, the latter being more or less freeflowing in character so that they can be packaged, shipped or storedbefore use. The dry powder thus obtained can also be used in coatingsbased on organic solvents provided that the shell component of thecore/shell particles is not soluble in the organic solvent.

Besides being useful in water-based paints based on vinyl or acrylicpolymer lattices or aqueous solutions of vinyl or acrylate polymers, toreplace all or part of opacifying pigments heretofore used, especiallytitanium dioxide, microvoid containing core/shell polymer particles ofthe present invention may be used for similar purposes in other coatingsystems, including resin formaldehyde condensation products ofthermosetting type, such as phenoplast and aminoplast, including ureaformaldehyde, and melamine formaldehyde, and other condensates, forexample, water dispersible alkyd resins.

An opacified composition adapted for coating and/or impregnanting asurface may comprise an aqueous dispersion of water-insoluble emulsionvinyl addition polymer having an apparent T_(g) of from about 5° C. to25° C., and water-insoluble core shell particles of the presentinvention at a pigment volume concentration of at least about 5%,inorganic pigment, such as titanium dioxide, and optional extender.

In another embodiment the process of the present invention may beemployed to encapsulate organic target materials such as organiccompounds, which are relatively insoluble in water but soluble in theblend of solvent and monomer used to prepare the core emulsion. Thematerial to be encapsulated is included in the mixture used in preparingthe core emulsion. Examples of organic target materials which may beencapsulated by the process of the present invention include pesticides,biocides, herbicides, fungicides, insecticides, dyes, inks, colorants,chelating agents, perfumants, pharmaceuticals and the like. Any liquid,solvent-soluble solid, or the like which is sufficiently hydrophobic, sothat when mixed with aqueous dispersion of core emulsion it tends tobecome substantially distributed within the core emulsion phase, anddoes not inhibit polymerization of the core emulsion, may bemicroencapsulated by the present technique. Aqueous dispersions ofmicroencapsulated pesticides, biocides, herbicides, fungicides,insecticides, and pharmaceuticals are especially useful in preparingcontrolled release formulations, in which the encapsulated material isslowly released from the microcapsule, as by diffusion through themicrocapsule walls. Aqueous dispersions of microencapsulated pesticides,biocides, herbicides , fungicides, insecticides and the like may beincluded with other agricultural chemicals such as emulsifiableconcentrates of pesticides in tank mixes and sprayed using conventionalapplication equipment. Microencapsulation may result in reduced toxicityand extended effective application lifetime for pesticides and othertoxic materials.

Examples of organic target compounds with biocidal activity includewater-insoluble herbicidal diphenyl ethers such as oxyfluorfen andwater-insoluble isothiazolone biocides such as2-n-octyl-3-isothiazolone.

When employed to encapsulate inks, dyes and colorants and the like, thecore/shell particles of the present invention may be released byapplication of mechanical force to the core/shell particles, or whichotherwise breaks, melts, dissolves or otherwise destroys the integrityof the microcapsule shell. Alternatively, the shell of the core/shellpolymer shell may be permeable to the target organic compound, resultingin slow continuous release of the target material from the core/shellparticles.

Core/shell particles of the present invention encapsulating targetorganic materials such as biocides may be used to prepare microberesistant coatings compositions, and especially water-based coatingscompositions. For example, biocide encapsulated in an aqueous dispersionof water-insoluble core/shell particles of the present invention may bemixed with pigments, extenders, vinyl addition latex polymer, and thelike, to form a coating composition. Core/shell particles may beprepared which both contribute opacity to the film formed by the coatingcomposition in which they are included and slowly release biocidallyactive material to help preserve the coating film from microbial attack.

When employed to encapsulated target materials, it is preferred thatratio of solvent to monomer blend used to prepare the core particles beabout 1:2.7.

In preparing microencapsulated target materials, a single stage processwhich does not employ additional monomer is preferred.

Core/shell particles of the present invention may also be prepared inthe presence of an organic target material containing chemicallyreactive functional groups such as isocyanate functional groups andepoxy groups.

    ______________________________________                                        EA               ethyl acrylate                                               MMA              methyl methacrylate                                          AN               acrylonitrile                                                MAA              methacrylic acid                                             S                styrene                                                      BA               butyl acrylate                                               ALMA             allyl methacrylate                                           ______________________________________                                    

The following examples are illustrative of the present invention whichis in no way limited thereby. In the examples the parts and percentagesare by weight and temperatures are in degrees Celsius unless otherwisestated.

EXAMPLE 1 Preparation of Core/Shell Particles

A core emulsion is prepared by adding, to 200 parts of water, 100 partsof a solvent mixture composed of 70 parts Isopar G isoparaffinhydrocarbons (Isopar is a trademark of Exxon) and 30 parts n-pentanol,100 parts of the initial (first stage) monomer mixture (5 parts ethylacrylate, 92.5 parts methyl methacrylate, and 2.5 parts methacrylicacid), 6 parts of dioctylphthalate, 0.85 parts Monowet MO-70E surfactant(Monowet is a trademark of Monom Industries, Inc.) and 3.5 parts AlperoxF lauryl peroxide (Alperox is a trademark of Pennwalt). The mixture isthen emulsified at high shear (18,000 rpm) using a Micro-Mixeremulsifier, (manufactured by Charles Ross & Son Company, Hauppauge,N.Y.) for 7-10 minutes. 300 parts of core emulsion is mixed with 75parts of water at room temperature in a 4-neck-round bottom flaskequipped with a stirrer, thermometer and temperature regulator,condenser, and nitrogen stream. Under nitrogen, the temperature of thereaction mixture is raised to 85-87° C. and this temperature ismaintained for 1/2 hours. 6.5 parts of ammonia (5.6%) is then addedthrough one of the necks and the reaction mixture is stirred for 1/2hour. Gradual addition of the additional (second stage) monomer mixtureis then begun. The second stage monomer mixture contains 10 parts butylacrylate, 87 parts methyl methacrylate and 2 parts allyl methacrylate.73 parts of this mixture are gradually added over a 90-100 minute periodto the reaction flask containing the initial core/shell particles.One-half hour after initiating the second stage monomer feed, 2.2 partsof dilute ammonia (5.6%) are added to the reaction flask. One hour afterthe second stage monomer feed is initiated another 2.2 parts of diluteammonia (5.6%) is added. After the second stage monomer mixture feed hasbeen completed, the temperature of the reaction flask is maintained for1/2 hour. The reaction mixture is then cooled and decanted from thereaction flask.

Preparation of Polymer Film and Measurement of Opacity

An aqueous dispersion of core/shell particles is mixed with acommercially available film-forming acrylic latex polymer, RHOPLEX®AC-64 polymer (RHOPLEX is a trademark of Rohm and Haas Company), in a15-85 ratio (based on the weight of solids of each polymericdispersion). The mixture of core/shell particles and film-forming latexpolymer particles is diluted to a final total solids of 40%. A film isdrawn down over black polyvinyl chloride sheets having a matte finishusing an applicator having a 5 mil (0.0127 cm) aperture to give anominal film thickness of 5 mils. Two draw downs are made, one fordrying under low relative humidity (approx. 30%), the other under highhumidity (about 70%). The two films are dried overnight. Lightscattering from the dried films is then measured using a GardnerColorgard 45% Reflectometer (Gardner Laboratories, Inc.). Kubelka-Munkscattering coefficients (s/ml) are calculated for the dried films by themethod of P. B. Mitton and A. E. Jacobsen, Official Digest, Vol. 35,Federation of Paint and Varnish Production Clubs, ODFPA, Sept. 1963, pp871-911.

Using the method of Example 1 above, aqueous dispersions of core/shellparticles were prepared and their ability to opacify a model film wasmeasured as described above.

Table I reports the results of varying the monomer composition of thefirst stage on the film opacity for core/shell particles prepared usingthe process of Example 1.

                  TABLE I                                                         ______________________________________                                        Effect of First Stage Monomer Composition on Film Opacity                     First Stage.sup.2     Film Opacity                                            Example                                                                              Composition        S/mil   % Collapse                                  ______________________________________                                        1      5 EA/92.5 MMA/2.5 MAA                                                                            .439     3                                          2      10 BA/87.5 MMA/2.5 MAA                                                                           .336    34                                          3      10 EA/87.5 MMA/2.5 MAA                                                                           .397    31                                          4      97.5 MMA/2.5 MAA   .371    21                                          5      5 AN/92.5 MMA/2.5 MAA                                                                            .362    17                                          6      5 S/92.5 MMA/2.5 MAA                                                                             .400    19                                          ______________________________________                                         .sup.1 The process used employs solvent (hydrophobic plus hydrophilic),       initial monomer (first stage), and additional monomer (second stage) in a     weight ratio of 1:1:1. The solvent is a mixture of Isopar G isoparaffins      and npentanol in a weight ratio of 7:3. 0.3% Monowet MO70E surfactant         (based on the weight of the organic phase in the initial stage) is            employed.                                                                     .sup.2 Second stage monomer composition is 10 BA/88 MMA/2.0 ALMA.             .sup.3 The % collapse is determined as follows:                               ##STR1##                                                                 

The data in Table II give the effect of varying the composition of thesecond stage of the core/shell particles on film opacification.

                                      TABLE II                                    __________________________________________________________________________    Effect of Second Stage Monomer Composition on Film Opacity                    Monomer Composition.sup.1       Opacity                                       Example                                                                            Stage I       Stage II     S/mil                                                                             % Collapse.sup.2                          __________________________________________________________________________    2    10 BA/87.5 MMA/2.5 MAA                                                                      10 BA/88 MAA/2 ALMA                                                                        .336                                                                              34                                        7    5 S/92.5 MMA/2.5 MAA                                                                        10 BA/88 MMA/2 ALMA                                                                        .400                                                                              19                                        8    5 S/92.5 MMA/2.5 MAA                                                                        10 EA/88 MMA/2 ALMA                                                                        .382                                                                              14                                        9    5 S/92.5 MMA/2.5 MAA                                                                        5 S/93 MMA/2 ALMA                                                                          .409                                                                               9                                        10   5 EA/92.5 MMA/2.5 MAA                                                                       5 2/93 MMA/2 ALMA                                                                          .349                                                                              10                                        __________________________________________________________________________     .sup.1 The process used employs solvent (hydrophobic plus hydrophilic),       initial monomer (first stage), and additional monomer (second stage) in a     weight ratio of 1:1:1. The solvent is a mixture of Isopar G isoparaffins      and npentanol in a weight ratio of 7:3. 0.3% Monowet MO70E surfactant         (based on the weight of the organic phase in the initial stage is             employed.                                                                     .sup.2 The % collapse is determined as follows:                               ##STR2##                                                                 

Table III gives the effect of varying the solvent blend on theproperties of core/shell particles prepared by the process of Example 1.

                                      TABLE III                                   __________________________________________________________________________    Effect of Hydrophobic Solvent on Film Opacity.sup.1                           Solvent Properties                                                                                Composition (%)                                                         50% Dist. Cyclo-  Film Properties                               Example                                                                            Solvent  Temp. Paraf                                                                             paraf.                                                                            Arom.                                                                             S/mil                                                                             % Collapse.sup.7                          __________________________________________________________________________    11   Odorless Mineral                                                                       183   86  14      .222                                                                              32                                             Spirits                                                                  12   Mineral Spirits                                                                        172   48  51      .219                                                                              14                                             66/3                                                                     13   Isopar G.sup.3                                                                         163   93   7      .249                                                                              10                                        14   Isopar H.sup.3                                                                         181   94   7      .217                                                                              31                                        15   Norpar 12.sup.4                                                                        200   98   2      .268                                                                              41                                        16   Varsol.sup.5                                                                           172   46  40  14  .169                                                                              34                                        17   VM & P Naphtha.sup.6                                                                   122   49  41  10  .028                                                                              --                                        __________________________________________________________________________     .sup.1 The process used to prepare the aqueous dispersions of core/shell      particles employes solvent, initial monomer and additional monomer in a       weight ratio of 1:1.3:1. The solvent is a mixture of npentanol and            hydrophobic solvent in a weight ratio of 3:7. The monomer composition of      Example 1 is used in preparing the core/shell particles.                       .sup.2 "Mineral spirits 66/3" refers to Amsco Mineral Spirits 66/3; from     Union Chem. Div. of Union Oil Company.                                        .sup.3 Isopar is a trademark of Exxon.                                        .sup.4 Norpar is a trademark of Exxon. Norpar 12 solvent is a mixture of      highly pure normal paraffins, and has 13% by weight C10, 36% C11, 44% C12     and 7% C13 alkanes.                                                           .sup.5 Varsol is a trademark of Exxon.                                        .sup.6 VM & P naphtha is a narrow boiling fraction of petroleum.              .sup.7 See footnote 2 of Table II.                                       

Table IV gives the effect of varying the methacrylate acid level in thefirst stage on the film opacification for core/shell particles preparedusing the process of Example 1.

                  TABLE IV                                                        ______________________________________                                        Effect of Methacrylic Acid Level on Film Opacity                                                            % Collapse.sup.2                                Example  % MAA.sup.1  S/Mil   (high % RH)                                     ______________________________________                                        18       2.0          .02     (41).sup.4                                      19       2.5          .22/.25 32/7                                            20       3.0          .20     35                                              21       3.5          .02     (73).sup.5                                      ______________________________________                                         .sup.1 The process used to prepare aqueous dispersion of core/shell           particles employs solvent, initial monomer and additional monomer in a        weight ratio of 1:1.3:1. A solvent blend of odorless mineral spirits and      npentanol in a weight ratio of 7:3 is used. Example 18 has an initial         monomer composition of 10 BA/88 MMA/2 MAA and an additional monomer           composition of 10 BA/88 MAA/2 ALMA. In the succeeding examples, as the        level of MAA is increased, the level of MMA is correspondingly decreased.     .sup.2 The % collapse is determined as follows:                               ##STR3##                                                                 

Table V gives the effect of varying the allyl methacrylate level in thesecond stage composition on the film opacification of core/shellparticles prepared according to the process of Example 1.

                  TABLE V                                                         ______________________________________                                        Effect of ALMA Level on Film Opacity                                          Example  % ALMA.sup.1  S/Mil   % Collapse.sup.2                               ______________________________________                                        22       0             .201    27                                             23       0.5           .213    18                                             24       1             .235    22                                             25       2             .247     7                                             26       3             .192    32                                             27       4             .212    29                                             ______________________________________                                         .sup.1 The process used to prepare aqueous dispersions of core shell          particles employs solvent, initial monomer and additional monomer in a        weight ratio of 1:1.3:1. A solvent blend of colorless mineral spirits and     npentanol in a weight ratio of 7:3 is used. Example 22 has an initial         monomer composition of 10 BA/87.5 MMA/2.5 MAA and an additional monomer       composition of 10 BA/90 MMA. In the succeeding examples, as the level of      ALMA is increased, the level of MMA is correspondingly # decreased.           .sup.2 The % Collapse and Calculated Shell Thickness and Void Volume are      determined as for Examples 18-21 above.                                  

Table VI gives the effect of varying the level of surfactant employed inthe process of Example 1 on the film opacification of the core/shellparticles produced.

                  TABLE VI                                                        ______________________________________                                        Effect of Surfactant Level on Film Opacity                                             % Surfac-                                                                     tant/Org.             % Collapse                                     Example  Phase        S/Mil    (high % RH)                                    ______________________________________                                        28       0.3          .243     35                                             29       0.4          .264     19                                             30       0.5          .290     33                                             31        0.65        .244     24                                             32       0.8          .222/.247                                                                               32/7                                          ______________________________________                                         1. The process used to prepare aqueous dispersion of core/shell particles     employs solvent, initial monomer and additional monomer in a weight ratio     of 1:1.3:1. A solvent blend of odorless mineral spirits and npentanol in      weight ratio of 7:3 is used. The monomer composition is the same as           Example 2 above. Example 28 is prepared using 0.3% Monowet MO70E              surfactant as a weight percentage of the organic phase in the initial         polymerization stage.                                                         2. The % Collapse, is determined as for Examples 18-21 above.            

EXAMPLE A Encapsulation of Methyl Hexanoate

A core emulsion is prepared by adding, to 233 parts of water, 100 partsof a solvent mixture (55 parts Isopar G isoparaffins/30 partsn-pentanol/15 parts methyl hexanoate), 133 parts of monomer mixture(97.5 parts methyl methacrylate/2.5 parts methacrylic acid), 7 partsdioctyl phthalate, 1 part of Monowet-70E surfactant, and 4.7 parts ofAlperoxide-F lauryl peroxide initiator. The mixture is then emulsifiedby mixing at high shear (18,000 rpm) for 10 minutes using a RossMicro-Mixer Emulsifier. 250 parts of the core emulsion is transferred toa reaction vessel consisting of a 4-neck round-bottom flask equippedwith a stirrer, thermometer and temperature regulator, condenser and anitrogen stream. 62.5 parts of water is added to the reaction flask.Under nitrogen the temperature of the reaction mixture is brought to85-88° C. and maintained at that temperature for 1/2 hour. 6.2 parts ofdiluted ammonia (5.6%) is then added and the temperature is maintainedfor another 1/2 hour. Gradual addition of additional (second stage)monomer mixture is then begun. The monomer mixture consists of 52.2parts of a mixture of 98 parts methyl methacrylate to 2 parts of allylmethacrylate. The second stage mixture is added over a period ofapproximately 75 minutes. Approximately 25 minutes after beginning thegradual addition of second stage monomer, 2.1 parts of dilute ammonia(5.6%) is added. Approximately 50 minutes after initiating the gradualaddition of second stage monomer another 2.1 parts of dilute ammonia(5.6%) is added. The temperature of the raction flask is maintained for30 minutes after completion of the second stage monomer feed after whichthe reaction flask is cooled and the aqueous dispersion of core/shellparticles is decanted. The core/shell particles of this preparation givea film opacity of 0.28 s/mil. The hydrolysis rate of the encapsulatedmethyl hexanoate was measured at a pH of 11.5 using gas liquidchromatography. The half life of the encapsulated ester was 83 minutesin comparison with the half life of 17 minutes for unencapsulated ester.

EXAMPLE B Encapsulation of SKANE Biocide

A core emulsion is prepared by adding to 367 parts of water 100 parts ofa solid mixture composed of 55 parts odorless mineral spirits, 30 partsn-pentanol and 15 parts SKANE M-8 (SKANE is a trademark of Rohm and HaasCompany) biocide. 268 parts of a monomer mixture composed of 10 partsbutyl acrylate, 88.5 parts methyl methacrylate and 2.5 parts methacrylicacid are added, as are 11 parts dioctyl phthalate, 2.6 parts MonowetMO-70E surfactant, and 9.3 parts lauroyl peroxide initiator. The mixtureis then emulsified at high speed (18,000 rpm) using a Ross Micro-MixerEmulsifier for 10 minutes. 250 parts of the core emulsion is transferredto a raction vessel as in Example 1. 62.5 parts of water is added to thereaction vessel. Under nitrogen the temperature of the reaction mixtureis brought to 85-88° C. and the temperature is maintained for 60minutes. 7.8 parts of dilute ammonia (5.6 %) are then added and thetemperature is maintained at 85-88° C. for an additional 30 minutes. Thereaction mixture is then cooled and decanted. Example B is repeatedexcept that a solvent mixture of 40 parts odorless mineral spirits, 30parts n-pentanol and 30 parts SKANE biocide is employed yielding ExampleB-1.

Aqueous latex paint is prepared according to the following formulation:

    ______________________________________                                                           Parts by Weight                                            ______________________________________                                        Materials                                                                     water                58                                                       methyl CARBITOL      59                                                       QR-681M dispersant   7.1                                                      TRITON ® N-57 surfactant                                                                       4.0                                                      Colloid 643 defoamer 1.0                                                      TiPure R-902 titanium dioxide                                                                      225                                                      Minex 4 pigment      160                                                      Icecap K pigment     50                                                       ______________________________________                                         The above ingredients are ground at high speed (3800-4500 rpm) for 10-15      minutes and the let down at slower speed with the following additional        ingredients.:                                                            

    water                50                                                       Rhoplex AC-64 polymer emulsion                                                                     306                                                      Colloid 643 defoamer 3.0                                                      Texanol coalescent   9.0                                                      NH.sub.4 OH          2.9                                                      Natrosol 250 MHR thickener                                                                         199.6                                                    water                22.1                                                     Formulation Constants                                                         Initial viscosity, KU                                                                              88                                                       pH                   9.5                                                       QR-681M is a dispersant and a product of Rohm and Haas Company.               TRITON ® N-57 surfactant is a product of Rohm and Haas Company. CAS       Registry No. 901645-9                                                         Colloid 643 is an antifoam agent and a product of Colloids, Inc.              TiPure R902 titanium dioxide is a product of E. I. DuPont De Nemours Co.      Minex 4 clay is a product of Indusmin Co.                                     Icecap K is a product of Burgess Pigment Co.                                  RHOPLEX ® AC-64 polymer latex emulsion is a product of Rohm and Haas      Company.                                                                      Natrosol 250 MHR cellulosic thickener is a product of Hercules, Inc.     

This paint was spiked with encapsulated biocide of Example B to providea test paint with 2 grams of active ingredient/1200 gms of paint.

Table VII gives the result of encapsulating the biocide on its heat-agestability in paints. The heat-aged stability is measured by placing thetest paint in a 60° C. oven for aging. At appropriate intervals samplesare taken and analyzed for SKANE M-8 biocide via a GLC technique.

                  TABLE VII                                                       ______________________________________                                        % of Initial Skane M-8 Biocide Remaining                                      First Series     Second Series                                                       Uncapsu- Encapsu-        Unencap-                                                                             Encap-                                 Days at                                                                              lated    lated    Days   sulated                                                                              sulated                                60° C.                                                                        Biocide  15%      at 60° C.                                                                     Biocide                                                                              15%.sup.1                                                                          30%.sup.1                         ______________________________________                                        0      100      100      0      100    100  100                               4      81.5     100      5      32     100  100                               7      0        100      9      0      100  100                               10     --       99       12            100  100                               13              100                    100                                    16              99       16            100  52                                20              99       20            100  0                                 24              84                     100                                    27              91       26            100                                                             30            100                                    31              76                     100                                                             35            100                                                             40            100                                                             44            100                                                             51            45                                     ______________________________________                                         .sup.1 % SKANE M8 biocide on solvent core.                               

The results in Table VII indicate that encapsulation of the biocide bythe process of present invention increases the heat-age stability of thebiocide in paint compositions. Heat-age stability is believed to bepredictive of long-term room temperature storage stability of paintformulations.

EXAMPLE C Encapsulation of GOAL® Herbicide

A core emulsion is prepared by adding to 368 parts of water 100 parts ofsolvent mixture consisting of 45 parts Isopar G, isoparaffins, 30 partsn-pentanol and 25 parts technical grade GOAL oxyfluorfen herbicide (GOALis a trademark of Rohm and Haas Company). 270 parts of a monomer mixture(5 parts ethyl acrylate/92.5 parts methyl methacrylate/2.5 partsmethacrylic acid) is added to the core emulsion mixture as are 11 partsdioctyl phthalate, 2.5 parts Monowet MO-70E surfactant, and 9.4 partsAlperoxide F lauryl peroxide initiator. The mixture is then emulsifiedat high shear (18,000 rpm) for about 7 to 10 minutes using a RossMicro-Mixer Emulsifier.

250 parts of the core emulsion are transferred to the reaction vessel ofExample 1 and 24.2 parts of water is added. Under nitrogen thetemperature of the reaction mixture is brought to 85-88° C. and theremaintained for 60 minutes. Subsequently 7.8 parts of dilute ammonia(5.6%) is added to the reaction mixture and the temperature ismaintained for another 30 minutes after which the reaction mixture iscooled and decanted to give Example C-1.

The same procedure is repeated substituting 50 parts by weight and 70parts by weight of GOAL herbicide to yield Examples C-2 and C-3respectively.

The procedure of Example C is repeated substituting (15% by weight onIsopar G/n-pentanol core solvent) a haloketone herbicide disclosed inU.S. Pat. No. 3,661,991, namelyN-(1-methyl-1-ethyl-3-chloro-acetonyl)-3,5-dichlorobenzamide, yieldingExample D.

The procedure of Example C is repeated substituting (15% by weight onIsopar G/n-pentanol core solvent) a triazole fungicide, namely,alpha-(4-chlorophenyl)-butyl-1H-1,2,4-triazole-propanenitrile yieldingExample E.

We claim:
 1. A process for encapsulating at least one organic targetmaterial in water-insoluble core/shell particles comprising(a) preparingcore emulsion by emulsifying in water at high shear constituentscomprising(1) organic target material to be encapsulated, (2) at leastone hydrophilic solvent, (3) initial monomer comprising at least twopolymerizable mono-alpha, beta-ethylenically unsaturated compoundswherein said initial monomer includes from about 2 to 4 percent byweight, based on total weight of said initial monomer, of alpha,beta-ethylenically unsaturated carboxylic acid monomer, (4) hydrophobicanionic surfactant, (5) water-insoluble emulsion stabilizer, (6)water-insoluble thermal polymerization initiator, and wherein saidorganic target material and hydrophilic solvents are non-solvents forpolymer prepared by polymerizing said initial monomer, (b) heating saidcore emulsion to polymerize said initial monomer thereby forming coreparticles, and (c) adding at least one base selected from the groupconsisting of ammonia and the non-nucleophilic organic amines therebyneutralizing polymerized carboxylic acid and forming core/shellparticles.
 2. The process of claim 1 wherein said core emulsion isprepared from constituents additionally comprising at least onehydrophobic solvent which is a non-solvent for the polymer prepared bypolymerizing said initial monomer.
 3. The process of claim 2additionally comprising adding additional monomer whereby saidadditional monomer is polymerized on the core/shell particles.
 4. Theprocess of claim 48 wherein the additional monomer is selected to yielda polymer having a calculated glass transition temperature greater thanabout 70° C.
 5. The process of claim 4 wherein aid additional monomercomprises at least one multi-alpha,beta-ethylenically unsaturatedmonomer.
 6. The process of claim 5 wherein said multi-alpha,beta-ethylenically unsaturated monomer comprises no more than about 5percent by weight of said additional monomer.
 7. The process of claim 4wherein said additional monomer comprises at least 80% by weight, basedon the total weight of said additional monomer, of methyl methacrylate.8. The process of claim 2 wherein the initial monomer is selected toyield polymer having a calculated glass transition temperature greaterthan about 70° C.
 9. The process of claim 8 wherein the initial monomercomprises at least 80% by weight, based on the total weight of saidinitial monomer, of monomer selected from the group consisting of methylmethacrylate, styrene, and mixtures thereof.
 10. The process of claim 9wherein the hydrophobic solvent is selected from the group consisting ofthe acyclic paraffinic hydrocarbons, mixtures of the acyclic paraffinichydrocarbons and cyclic paraffinic hydrocarbons, and mixtures of acyclicparaffinic hydrocarbons, cyclic paraffinic hydrocarbons and aromatichydrocarbons wherein said mixtures contain less than about 10% byweight, based on the total weight of the mixture, of aromatichydrocarbon.
 11. The process of claim 10 wherein the hydrophilic solventis selected from the group consisting of the isomers of butanol,pentanol, hexanol, and methyl isobutyl carbinol, and mixtures thereof.12. The process of claim 11 wherein the 50% distillation temperature ofsaid hydrophobic solvent is from about 150° C. to 200° C.
 13. Theprocess of claim 2 wherein said initial monomer comprises up to about 10percent by weight, based on the total weight of said initial monomer, ofnonionizable monomer selected from the group consisting of ethylacrylate and acrylonitrile and mixtures thereof.
 14. The process ofclaim 13 wherein said nonionizable monomer is ethyl acrylate.
 15. Theprocess of claim 2 wherein the anionic surfactant is selected from thegroup consisting of the alkali metal salts of the di(C₇ c₂₅)alkylsulfosuccinates and the alkyl aryl polyalkoxy sulfonates and alkyl arylpolyalkoxy phosphates.
 16. The process of claim 15 wherein the anionicsurfactant is selected from the group consisting of the alkali metalsalts of dioctyl sulfosuccinate and of dodecyl benzene sulfonate. 17.The process of claim 2 wherein the water-insoluble emulsion stabilizeris an organic compound having a molecular weight of less than about 500and a water solubility of less than about 10⁻⁴ g/l.
 18. The process ofclaim 17 wherein said water-insoluble emulsion stabilizer is selectedfrom the group consisting of di(C₄ -C₁₀)alkyl phthalates, dibutoxyethylphthalate, n-butyl benzyl phthalate, dimethyl cyclohexyl phthalate,dicyclohexyl phthalate, diphenyl phthalate, dipropylene glycoldibenzoate, diethylene glycol dibenzoate, triethylene glycol di(2-ethylbutyrate), di(2-ethylhexyl)adipate, di-isooctyl azelate,di-(2-ethylhexyl) azelate, di-n-butyl sebacate, 1-chlorododecane,hexadecane, and mixtures thereof.
 19. The process of claim 17 whereinsaid water-insoluble emulsion stabilizer comprises at least about 0.25percent by weight of the organic phase of the core emulsion.
 20. Theprocess of claim 2 wherein the ratio of the weight of water-insolublethermal polymerization initiator to the total weight of initial monomeris from about 0.1:100 to 5:100.
 21. The process of claim 20 wherein theratio of the weight of said water-insoluble thermal polymerizationinitiator to the total weight of initial monomer is from abut 2.5:100 to4.0:100.
 22. The process of claim 20 wherein said water-insolublethermal polymerization initiator is lauryl peroxide.
 23. The process ofclaim 2 wherein the hydrophobic organic target compound to beencapsulated has at least one isocyanate functional group.
 24. Theprocess of claim 2 wherein said organic target compound to beencapsulated has at least one epoxy group.
 25. The process of claim 1wherein the organic target material to be encapsulated has biocidalactivity.
 26. An encapsulated biocide comprising an aqueous dispersionof the water-insoluble core/shell particles prepared according to theprocess of claim
 25. 27. The process of claim 1 wherein the organictarget material is selected from the group consisting of2-n-octyl-3-isothiazolone, oxyfluorfen and mixtures thereof.
 28. Theprocess of claim 27 wherein said hydrophobic organic target compound isoxyfluorfen.
 29. A coating composition comprising core/shell particlesproduced according to the process of claim 27 pigments, extenders andvinyl addition latex polymer.
 30. A sprayable agricultural herbicidecomposition comprising herbicidally effective target materialencapsulated according to the process of claim 1.